Stabilized yarn



Oct. 18, 1960 G. PITZL 2,956,330

STABILIZED YARN Filed March 28, 195s INVENTOR GILBERT PITZL ATTORNEY United States Patent O sTABnJzED YARN Gibert Pitzl, Chattanooga, Tenn., assigner to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Mar. 2S, 1958, Ser. No. 724,613

16 Claims. (Cl. lZ13-Jil) This invention relates to iilamentary structures composed of synthetic linear polyamides, and has particular reference to a process wherein such structures are drawn to increased length and orientation. More specifically, this invention relates to a process for improving the uniformity and dimensional stability of drawn polyamide filaments.

lt is known that freshly drawn nylon yarn has a tendency to undergo a gradual lengthwise retraction on standing. If the yarn is not free to retract, ie., when such yarn is restrained to a fixed length, tension in the individual filaments gradually increases. When this effect occurs in the multiple layers of yarn Wound onto a solid package, tremendous compressive forces are developed. Responsive to these forces, the inner yarn layers on the package are crushed to an extent suliicient to permit retraction of the individual filaments. The filaments which are permitted to retract acquire higher denier, lower modulus, higher break elongation, increased dyeability, and lower boil-off shrinkage, as compared to the filaments which are restrained and cannot retract. There results, therefore, a difference in yarn properties radially throughout such a package. Moreover, the magnitude of such compressive forces necessitates the use of package cores of extreme strength, thereby precluding the use of the inexpensive disposable cores commonly used in the textile trade.

In packaging drawn nylon yarn it is common to use a vvindup comprising a spindle bearing a bobbin, associated with a conventional ring and traveler combination which is traversed over the package being formed. The customary package has a double-tapered contour, which is produced by diminishing the traverse stroke of the lay rail, which results in progressively more yarn being wound near the center of the package than near the ends. Although this type of package has many advantages, such as package stability, ease of manufacture, facile yarn takeoff, and the like, it is particularly prone to the abovementioned diiculties. In addition to the expected differences in yarn properties radially through such a package, there arise dierences in the properties between yarn wound on the tapered ends of the package (which is not compressed and hence not free to retract) and yarn wound near the center of the package (which is free to retract due to the compressive force of the yarn layers wound upon it).

When yarn 'om a tapered package is woven into fabric, there is observable the fabric defect known as pirn taper barr, which appears as a streakiness visible in both dyed and undyed fabric. The streakiness may be due to differences in dye depth, denier variations, or variations in :fabric construction related to Variable shrinkage in the warp yarn, The frequency of these streaks has been found to correlate with the period of the traverse stroke during packaging.

A measurement of residual shrinkage (loss in length of yarn produced by exposing relaxed skeins of such yarn to boiling water) of yarn taken from such tapered pack- 'ice ages has shown that there is a significant difference in residual shrinkage depending on the location of the yarn sample in the package. The frequency of residual shrinkage variation also has been found to coincide with the streaks observed in woven fabric. The magnitude of the shrinkage variation has been shown to be proportional to the severity of the streaks. In order to produce a more uniform yarn, it is apparent that dierential shrinkage throughout the package must be reduced.

It is known to reduce residual shrinkage of nylon yarn by heating such yarn under conditions of minimum tension, in order to permit the yarn to retract. A typical process Iis described by Lewis (U.S. 2,199,411), wherein nylon yarns are treated with dry heat so that residual shrinkage is reduced from about 10% to less than 2%. Such yarn exhibits reduced residual shrinkage by virtue of having undergone substantial shrinkage prior to packaging. However, such procedures do not permit reduction of differential yarn shrinkage throughout the package (which might be expected to be reduced by an extent proportional to the reduction in over-all residual shrinkage), and yarn which is preshrunk according to these procedures incurs an undesirable reduction in initial modulus. Accordingly, such yarn exhibits an increased sensitivity to minor tension variations which occur during its subsequent handling and low winding tension during packaging is necessary, resulting in poor package formation and stability. Moreover, fabrics woven from such yarn have a pronounced tendency to exhibit a defect known as quill barr, which occurs as a result of the tension variations encountered during filling winding, in the preparation of loom quills. Finally, such yarn exhibits a wide variety o-f fabric defects catagorically known as loom streaks, all of which arise due to the tension variations encountered during weaving. As a result of the increased sensitivity of the preshrunk yarns, and of the numerous limitations imposed on the subsequent handling operations due to such sensitivity, these methods of reducing residual yarn shrinkage are considered unattractive.

Alternatively, it is known that nylong yarn crimp, twist, and similar conformations may be set by treatment with heating aud/or swelling agents. Miles (U.S. 2,307,846) proposes to reduce yarn residual shrinkage by setting the yarn at constant length. Residual shrinkage is indeed reduced by setting, but Miles preferred procedure comprises setting the yarn on the package, a practice which accentuates differential shrinkage and results in increased fabric barr. In addition, the prolonged exposures which are required to set the yarn preclude utilizing such a process in a continuous operation at present-day process speeds. As a result of such diiiicuties, setting as a means to reduce residual yarn shrinkage has met with very limited commercial acceptance.

Initial modulus is a useful measure of yarn resistance to lengthwise deformation, and is highly indicative of yarn behavior during subsequent packaging, on the package, and in subsequent textile operations such as twisting, quilling, weaving, and knitting. Yarn with high values of initial modulus is relatively insensitive to tension variations encountered during these operations; conversely, yarn with lower values o'f initial modulus is noticeably sensitive to such tension variations. Hence, it can be readily predicted that yarn having reduced initial modulus, e.g., a yarn which has been relaxed, will form poorer quality fabrics, exhibiting the variety of streaks and barr mentioned earlier, :as compared to yarn having a high or retained initial modulus.

One object of this invention is to provide a process for stabilizing freshly drawn polyamide vfilaments in a rapid and continuous manner.

Another object of this invention is to provide a process .is, therefore, a high-tension process.

Vconditions of heat and/ or moisture.

for preparing leshly drawn yam having reduced residual shrinkage and differential shrinkage achieved with undirninished initial modulus. t

A further object is to provide means for winding a nylon package from freshly drawn yarn, from which fabrics of a high `degree .of unifo'rmity can be woven.

A still further object is to provide an improved package of nylon yarn which has uniform residual shrinkage throughout.

Still another object is a stabilized freshly drawn nylon yarn which can be wound onto an inexpensive, disposable package core without distorting the core.

These and other objects, together with the means for accomplishing them, will appear hereinafter.

According to this invention freshly drawn polyamide filaments are relaxed Without an undesirable reduction of initial modulus by coupling such relaxation with a setting step. The freshly drawn filaments are continuously (a) heat-set at substantially constant length, and (b) subjected to controlled relaxation of from about 2 to about V% based on the filament length prior to retraction, and thereafter wound onto a package. Steps (a) and (b) may occur in either order; preferably, vthe laments are relaxed from about 6% to 10% after drawing prepackaged or lagged yarn, and relaxed from about 2% to 6% after drawing freshly formed or as-spun yarn. y A preferred embodiment of the invention comprises setting pre-packaged polyamide filaments with superheated steam at 175 C. to about 225 C. for less than about a second, relaxing the filaments to effect a length reduction of about 7% to 9%, and thereafter continuously winding the resulting stabilized filaments onto a package. Y Another preferred embodiment of the invention comprises setting freshly formed polyamide filaments with dry heat at 170 C. to about 250 C. for less than about a second, relaxing the filaments to effect a length reduci ythe practice of the present invention.

yFigure 2 illustrates the general contour ofV a tapered yarn package wherein differential shrinkage and other property variations occur.

Figure 3 shows in schematic section an oven useful in heating a running yarn line.

Figure 4 shows in schematic section ya jacket useful for treating a running yarn line with steam.

Figure 5 shows schematically an apparatus useful for setting a running yarn line with steam or similar heat transfer agents.

Figure shows a preferred arrangement of apparatus for accomplishing the process of this invention.

Referring to Figure l, undrawn nylon yarn 1 is withdrawn from package 2, passes through the pigtail guide 'Y 3, and is then passed in multiple wraps abolut driven feed .tion of about 2% to 4%, and thereafter continuously winding the resulting stabilized filaments onto a package.

This invention is applicable to any polyamide strands including'ilaments, fibers, threads, yarns, 'and the like lamentary structures. The term yarn will be used hereinafter as exemplary of all such structures, since in that form the invention has its greatest utility.

The term setting as employed herein refers tothe yprocedure wherein yarn is subjected to' the action of lheat while'restrained to substantially constant length 4and ried to extremes, leads to a permanent orientation of polymer molecules and increased Vcrystallinity. Setting in accordance with this invention -is carried out only to an 'extent sufficient to stabilize the yarn and yet permit a further substantial reduction in residual shrinkage via relaxation without the usual decrease in modulus. -It is important that such setting Vbe not complete;-the yarn should retain a measure of residual shrinkage so that, depending onits ultimate use, it can be further set, for

Setting, when carexample, in fabric form, upon encountering more stringent f SuchV post-setting is an essential practice in preparing most fabrics.

The term relaxation is self-explanatory, often synonymous with shrinking and refers to the procedure wherein yarnY is subjected 'tothe action of heat to produce a controlled reduction in length. YItvs, therefore, a low- Vtension process. Both setting andV relaxation-may be carried out incrementally.

The term stabilization refersv hereintd a two-step procedure'involving setting followed or preceded by a controlled relaxation, whereby'yarn is obtained. having substantially'reduced residualshrinkage and characterized -by its original or an increased initial-modulus.

Stabilized filaments 'prepared according to'this invention are characterized by having-significantly reduced residual shrinkage associated with undiminished high ,initial modulus and exhibit improved on-the-package uniformity of properties. Such a stabilized yarn can be roll 4 and its associated separator roll 5. `ln one embodiment yarn is supplied to guide 3 directly from a spinning machine rather than from a package. From feed roll 4 the undrawn yarn 1 makes one or more wraps about an externally heated, non-rotating snubbing pin 6 (Babcock, U.S. 2,289,232), and is drawn in fractional contact with pin 6 under the urging of draw roll 7 with its associated separator roll 8. Draw roll 7, of course, has a higher peripheral speed than feed roll 4, whence the yarn is elongated to several times its original length. From the draw roll 7V the yarn passes around the setting roll 9 and its associated separator roll 10, and thence to relaxing roll 11 and its separator roll 12. In zo'ne b between the draw roll 7 and the setting roll 9 there is placed the oven 17 of Figure 3 or similar means to be described in greater detail hereinafter. By maintaining the peripheral speed of draw roll 7 and setting roll 9 substantially the same, the yarn 1 is exposed to the conditions in oven 17 while being maintained at substantially constant length, and is thereby set. In zone c between the setting roll and the relaxing roll 11, there is similarly placed the oven 17 of Figure 3. By maintaining therrelaxing roll v1-1 at a peripheral speed less than the peripheral speed of the setting roll 9, the yarn is subjected -to controlled relaxation, accelerated by the influence of the atmosphere in oven 17. The yarn 1, after traversing the relaxing roll 11, passes through the pigtail guide 13 and is wound onto a tapered twister package 16 by means of ring 14 and traveler 15. The tension in the yarn wound onto package 16 is controlled by the weight of the traveler 15, as is well known in the twisting and winding art.

Both setting and relaxation can be carried out using the apparatus of Figure 3, wherein is shown the oven 17 furnished with the jacket 18 (conventional heating means not shown). `The extent of exposure of the yarn 1 to the existing conditions of temperature and humidity in the oven 17 is governed by the yarn rate of travel and by the length ofthe jacket 18. Where steam is employed as a setting or relaxing agent, the jacket 18 may be designed as shown in Figure 4, wherein the said jacket is furnished with a steam inlet 19,.a condensate trap 20, and a condensate return 21.

Since the operation of setting involves appreciably ylonger exposure times than relaxation, it is advantageous toemploy the apparatus shown in Figure 5. According to this arrangement, Vthe freshly drawn yarn 1 is passed in multiple'wraps about the draw roll 7 and its associated separator roll 8, thence into the setting oven 22, where the yarn is passed in multiple wraps about the idler rolls 25 land, 26. `Setting oven 22 may be provided with an inlet .23 for the heat transfer medium and condensate outlet 24. -After a sufficient'exposure to the setting conditions in the oven 22, the yarn is passed from the idler roll 25 back to the draw roll 7 and the separator roll 8. Exposure time of the yarn to the setting conditions existing in the oven 22 is governed by the rate of yarn travel, the distance between the separator rolls 25 and 26, and the number of yarn wraps about the rolls 25 and 26. After returning to the draw roll 7, the yarn is forwarded to the succeeding processing steps. When the apparatus of Figure 5 is employed in the process of Figure 1, the need for the setting roll 9 and its separator roll 10 is obviated. The yarn is then relaxed by adjusting the peripheral speed of the relaxing roll 11 a controlled amount less than the peripheral speed of the draw roll 7. The over 17 (Figure 3) is then placed between the draw roll 7 and the relaxing roll 11, zone b-c.

Setting and relaxing media useful in this invention include superheated or pressure steam, dry heat, inert liquids, mild swelling agents, land the like. Steam is a preferred agent for stabilizing, i.e., setting and relaxing, freshly drawn polyamide yarn, due to its effectiveness, cheapness, and safety. Using steam, stabilization occurs most rapidly for a given temperature of exposure, thus permitting the use of compact apparatus and thereby conserving machine space. Saturated or pressure steam is eective, but superheated steam is preferred. 'Steam temperatures of from 125 C. to 250 C. and above are satisfactory for most polyamides, and even higher temperatures are permitted it the polyamides is not low melting or susceptible to degradation. Due to abbreviated contact times, steam temperatures higher than the polymer softening point may be employed in particular instances. The preferred steam temperature range for setting is from about 175 C. to about 225 C., which temperatures permit setting with a minimum of diiculties, and in a rapid, continuous, and effective manner. The preferred steam temperature range for relaxation is from about 125 C. to 175 C.

Yarn setting is effected at substantially constant yarn length. By substantially constant length is meant that the yarn during setting is restrained or prevented from undergoing any decrease in its preset length. Such conditions are realized using the apparatus of Figure 5, or, according to Figure 1, by maintaining the peripheral speeds of the draw roll 7 and the setting roll 9 the same, provided there is substantially no slipping of the yarn thereon. Such slippage -is readily prevented by customary means known in the art such as by the use of pinch rolls, multiple wraps, or the like. When setting in zone a of Figure 1 (Example 5), a moderate increase in length is unavoidable, even though the greatest extent of drawing is localized on and about the pin 6. Accordingly, in such setting, an increase in length not exceeding about is permissible.

Results of equilibrium studies show that for any given setting agent, there exists an optimum setting temperature which, when achieved by the yarn during setting, results in a superior quality yarn after relaxation. Moreover, no additional benets are gained by permitting higher yarn temperatures, via increased temperature of the setting media or by increasing exposure time during setting. When using superheated steam, this optimum yarn setting temperature is about 125 C.; for dry heat the comparable temperature is about 180 C., hence the preference for using steam. Therefore, it is apparent that the setting time and temperature should besuch that the yarn temperature approaches the optimum setting temperature during setting, in order to receive a full meaure of the benets inherent in this invention. When employing 175 C. to 225 C. Superheated steam, exposure times less than about 1 second are usually sufficient. It should be readily appreciated that the setting time depends on the length of the yarn path in the setting oven and the rate of yarn travel through the oven. Accordngly, by adjustment of either of these variables, the setting time can be accurately controlled.

Although relaxation (or retraction, as mentioned earlier) occurs at room temperatures and humidities if suiicient time is allowed in going from roll 9 to roll 11 (Figure 1), at present-day processing speeds an unduly large distance would be required in order to permit the yarn to relax suciently. Accordingly, relaxation is accelerated by exposing the yarn to elevated temperatures.V

This is accomplished, as described hereinabove, while the yarn passes through oven 17, Figure 3. Relaxation is also accelerated in the presence of moisture, hence steam is a preferred relaxing agent. Dry heat may likewise serve to accelerate relaxation, although higher temperatures are occasionally required, as will be subsequently exemplied. Relaxation is preferably accomplished using C. to 175 C. superheated steam; such conditions permit the necessary relaxation in less than about one-tenth second. It should be noted that the exposure times reported herein for both relaxation and setting represent the minimum exposure under the stated conditions necessary to obtain the improvements characteristic of this invention. lIn a rapid continuous process, exposure times are preferably as short as possible. `Oi? course, longer exposures may be employed, even though substantially no additional benefits derive from such extended treatments. The maximum exposure to any given process condition is governed by the stability characteristics of the polymer from which the yarn has been prepared.

The preferred embodiments of this invention are illustrated by the following examples. All yarn contains 0.3% titanium dioxide added as a delustrant.

EXAMPLE 1 Using an apparatus arrangement substantially as shown in Figure 1, a 34 filament poly(hexamethylene adipamide) yarn is drawn at 5 62 yards per minute (y.p.m., peripheral speed of draw roll 7) to a iinal denier of 70, is thereafter continuously set, relaxed, and packaged. The yarn is set using 200 C., superheated steam, at varying exposure times. A constant controlled relaxation of 8% in C. steam is employed throughout this series, and the yarn is wound at 11 grams (0.16 g.p.d.) tension.

Setting is accomplished utilizing the oven 22 (Figure 5) cooperating with the draw roll 7 as shown. Accordingly, the need for the setting roll 9 of Figure 1 is obviated. The distance d (Figure 5) between centers of the idler rolls 25 and 26 is 18 inches, and since the yarn is traveling at 562 y.p.m., each complete yarn cycle about these rolls consumes 0.11 second time. By employing multiple passes about these rolls, yarn exposure time is accurately controlled and varied. Relaxation is effected using oven 17 of Figure 3, furnished with the jacket 18 of Figure 4 for use with the 150 C. superheated steam. The oven 17 is placed between the draw roll 7 and the relaxing roll 11. The peripheral speed of the relaxing roll 11 is 0.920 and that of the draw roll 17, permitting a controlled relaxation of 8%. The yarn speed through the oven 17 is 562 y.p.m., and the length or" the yarn path in the oven is 10 inches, hence contact time between steam and yarn is 0.03 second. summarizing the yarn drawn 1 passes from the pin 6 to the draw roll 7, into the steam chamber 22 wherein the yarn passes about the idler rolls 25 and 26, back to the draw roll 7, through the oven 17 to the relaxing roll 11, thence to the pigtail guide 13 and is packaged as described hereinabove.

Table I shows the yarn residual shrinkage, diierential shrinkage, and initial modulus as a function of setting time.

After treating the yarn samples under the conditions shown in Table l, packages of each sample are held 7 days at 75 F., 72% relative humidity prior to testing. The yarn samples are obtained by stripping yarn from the package shown in Figure 2 until the middle or barrel portion is reached (B-Figure 2). A sample 130 to 150 cm. in length is then removed and its length immediately measured, as described hereinbelow. Yarn removal is 1 Test yarn 70 denier, 34 filament, set and relaxed with 200 C. and 150 C. superheated steam, respectively, relaxed 8%, Wound at l1 g. (0.16 g.p.d.) tension.

- 2 Average residual shrinkage of all yarn on package.y

3 Maximum Taper-to-Barrel Difference in yarn residual shrinkage. 4 Relaxed 10%% in'l" C. supcrheated steam.

continued until the extreme taper portions of the bobbin are reached (positions A or C, Figure 2), and another sample of similar length is taken. The stripping is continued, taking samples from the extremities of the package and from theV longitudinal center of the bobbin, throughout the entire package;

Sample length is determined immediately after removal from the package; the ends of the yarn segment are knotted together, a Weight of about 0.1 g.p.d. is 'hung in the loop, and the length of this loop measured. After determining the initial length, the loop of yarn is submerged in boiling water for about 20 minutes, after which it is removed and dried about 25 minutes under the 0.1 g.p.d. tension. 'The length of the boiled-off loop is measured and the percent shrinkage is calculated based on the length of the original sample.

The initial modulus, represented by the symbol Mi, is dened as the ratio of change in stress to strain in the iirst reasonably linear portion of a stress-strain curve. The ratio is calculated from the stress, expressed either in force per unit linear density or force per unit area of the original specimen, Vand the strain expressed either as a fraction of the original length or as percent elongation. When strain is expressed in terms of elongation, the modulus equals 100 times the quotient (stress/strain). Initial modulus is also equivalent to 100 times the force in grams per denier required to stretch the specimen the first 1%. In this procedure, the modulus is determined at 10% elongation based on the slope of the Vcurve at 1%; the modulus at 1% yis calculated from this value. In either method, the factor 100 is a constant used to convert the modulus in grams per denier to a Whole number. In the present Work, the modulus is obtained from yarn stress-strain curves measured by the Instron Tensile Tester (Model TTB, supplied by Instron Engineering Corp., Quincy, Mass), which stretches the yarn at a constant rate of elongation. From the stress-strain curve, the slope of the initial straight line portion is determined graphically, and the modulus is calculated as 100 times the slope, divided by the denier of the sample. All yarn is conditionedfor 7 days at 75 F., 72% relative humidity prior to testing. These measurements are arcuate to about 0.5 g.p.d.

Test AA shows typical results obtained with yarn drawn in the conventional manner Without provision Jfor setting or relaxing. Such yarnis Ycharacterized by high initial modulus, high average shrinkage, and high diiferential shrinkage. Under the conditions of test AA, of course, yarn proceeds directly from'the draw roll 7 to Windup means 13-15 (Figure l), bypassing setting roll 9 'and relaxing roll 11. V

In test AB, the yarn is relaxed lOl/2% Without prior setting, bypassing the setting means of Figure 5. Other- Wise, conditions are the same as in test AA. In test AB, although yarn residual shrinkage and diiferentialshrinkn age are indeed reduced, such reduction is vunaccompanied by anrundesirable decrease in initial modulus, resulting in Va yarn which is sensitive to tension variations during subsequent handling. In tests AC to AF, setting at increasing exposure times is introduced prior to relaxation. In all cases, initial modulus remains high, and `average shrinkage and differential shrinkage are progressively reduced. In the optimum test AF, an exceptionally uniform yarn is produced. It may be reasonably assumed that the test yarn .in experiment AF Vhas achieved the optimum setting temperature, namely 125 C. since superheated steam is being employed as the setting agent. Only minor improvement in yarn uniformity is obtained by further increase in setting time (note test CE, Example 3).

VVYarn from the above tests AA, AB, and AE is com- Y pared with regard to maximum taper-to-barrel stretch tension differences. Stretch Vtension is a measurement of the tension `in grams developed in a yarn at a given degree of stretch, andoffers means for determining the uniformity of certain yarn properties, such as modulus and denier, throughout a package. Stretch tension is a measure of modulus uniformity at constant denier, and conversely, a measurement of denier uniformity at constant modulus. In the present examples, stretch tension is measured at 4% elongation. This evaluation may be performed on short-range yarn samples taken throughout the package, or it may be measured continuously, recording the maximum taper-to-barrel differential. To measure stretch tension continuously, yarn is taken from a conditioned -package (7 days at 75 F., 72% RH), passed from a feed roll around a a hysteresis brake-(Model 0-10 gram, supplied by the General Electric Co.), to insure constant tension during yarn feed, then passed through a Zimmer tensiometer head (supplied by Hans I. Zimmer, Frankfurt, Germany), and finally stretched 4% utilizing a stepped draw roll. Stretch tension in grams is recorded continuously, and from such information the maximum taper-to-barrel differential is determined. Results of these measurements are recorded in Table II.

Table II Test Yarn Stretch tension,

MTBD l AA 19 AB l2 AE- 3. 5

1 Maximum taper-to-barrel difference.

Results in Table II show the distinct improvement in vEXAMPLE, 2

Samples of 34 filament poly(hexamethylene adipamide) yarn are drawn to a final denier of 70, and then continuously set, relaxed, and wound into a package using the modified apparatus of Figure 1, described in Example 1. Setting is effected by 0.33 sec. exposure `to 200 C. superheated steam, followed by a controlled relaxation of 8% also linduced by such steam at 150 C. Winding tension is varied by changing the Weight of the traveler I5, as is Well known in the art of ring twisting. Results of these experiments are shown in Table III.

Initial Modulus (ap-d.)

Stretch Tension MTBD Percent Shrinkage Winding Tension (ap-d.)

Test

1 Test yarn 70 denier, 34 filament, set and relaxed with 200 C. and 150 C. superheatedsteam, Set for0.33 sec., relaxed 8%.

2 Control yarn, unset and unrelaxed.

3 Unset control. relaxed 101% in 150 C. superheated steam.

Results in Table III show the signiiicant improvement in yarn uniformity produced by the process of this invention. It is of particular interest to note the relative insensitivity of yarn from tests BB, BC, BD to varying winding tension. A yarn which has been merely relaxed (test BE), in addition to having reduced modulus, is quite Sensitive to winding tension, and the uniformity of such yarn deteriorates rapidly with increased winding tension. While the yarn of this invention shows little such sensitivity, it is preferred to wind at tensions between 0.05 g.p.d. and 0.30 g.p.d. At winding tensions below about 0.05 g.p.d., poor package formation results, with yarn tending to slough ofi the resulting package. The optimum tension for winding yarn treated according to this invention is about 0.16 g.p.d., which results in excellent package formation and stability. Despite some moderate yarn retensioning, unavoidable even in yarn treated according to this invention, yarn uniformity remains high when winding at tensions within the preferred range, as indicated.

EXAMPLE 3 In this experiment, setting is carried out after relaxation. The apparatus of Figure 1 is employed, modified to the extent that relaxation is accomplished between draw roll 7 and roll 9, using the oven 17 between these rolls. From roll 9 the yarn passes through an 18-inch steam jacket 18 (Figure 4) to the roll 12, which is maintained at the same peripheral speed as roll 9. Setting timein steam jacket 18 is controlled via the yarn rate of travel.

Utilizing this apparatus, a 34 lament poli/(hexamethylene adipamide) yarn of drawn denier of 70 is set and relaxed using 200 C. and 150 C. superheated steam, respectively. Peripheral speed of roll 9 is 0.920 that of roll 7; hence the yarn is relaxed a controlled 8% throughout this experiment. The results of these experiments `are recorded in Table 1V.

1 Test yarn 70 denier, 34 lament, set and relaxed with 200 C, and 150 G. superheated stream, respectively, relaxed 8%.

2 Unset control, relaxed 10l% in 150 C. super-heated steam.

It is apparent that setting after relaxing also results in uniform yarn (tests CC to CF). The relative insensitivity of these yarns to varying winding tension demon- 10 stratedv in Example 2 is also seen (tests CD to CF). No marked improvement in yarn property uniformly results from increased exposure time during setting (compare tests CC and CE), which indicates that the yarn in test CC has nearly reached the optimum setting temperature of about C.

EXAMPLE 4 The process of this invention can be accomplished using dry heat as the stabilizing agent. In this example, yarn is treated as described in Example l, using the modified apparatus of Figure 1 as indicated. Ovens 17 and 22 are heated by self-contained electrical heaters, so that the air temperature within each oven is about 450-550 C. The yarn is heated by convection and radiation. Care iS taken so that yarn does not accidentally contact the high temperature Surfaces of the heating elements. The above conditions are sufcient so .that the optimum yarn setting temperature, 180 C. for hot air, is achieved after exposures 0f less than about a second. Yarn is relaxed a constant and controlled 8%. There results from this treatment yarn having average shrinkage, differential shrinkage, and differential mechanical properties similar to the yarns of tests AE, BC, and CC. Initial modulus is retained throughout.

EXAMPLE 5 This example illustrates setting prior to relaxation in zone a of Figure 1. Using that apparatus, steam jacket 18 is placed between pin 6 and draw roll 7. Setting roll 9 is bypassed, hence relaxation is accomplished between draw roll 7 and relaxing roll 11. Setting time is controlled by yarn speed and length of the setting jacket 18.

With such an arrangement of apparatus, yarn is drawn, set, and relaxed according to tests AL and AF, Example 1. Substantially the same excellent results are obtained.

Setting in zone a is desirable since the yarn immediately after drawing is still warm, due to the heat and friction of drawing. Accordingly, shorter exposure time during setting is required. On the other hand, some additional drawing occurs during zone a setting, thereby reducing to a minor extent the control of the drawing operation. Thus, setting in zone a or in zone b is equally eflicacious, and the selection of either method is, therefore, determined by the needs of the practitioner of this invention.

EXAMPLE 6 Yarn from Example 1 is wound onto a cylindrical core after stabilization to form a straight (untapered) package of zero-twist yarn, utilizing conventional reciprocating traverse means. Stabilization is accomplished as indicated in Example 1 for the corresponding samples. Table V shows the average residual shrinkage and the range of residual shrinkage values throughout such packages.

Table V Percent shrinkage 1 Test 1 Average 1 Range 2 A A 9. 8 1. 60 AB 6.0 0.56 AC 6. 8 0.55 AD 6. 5 0. 30 AE 6. 4 0. 31 AF 5.6 0.23

1 Entries have same significance as in Table 1. 2 Maximum spread in residual shrinkage radially through the package Note that test yarns AD, AE, and AF are substantially improved with regard to residual shrinkage uniformity. This improvement is comparable to the uniformity achieved in Example 1 with tapered packages. Such improved residual shrinkage uniformity results in substan- 11 tial elimination of quill junction, the relatively longrange fabric-defect which stems from the random use of iilling yarn taken from different portions of a supply package during the preparation of loom quills. With a stabilized yarn, properties are the Vsame throughout the package, hence the problem of quill junctions is avoided.

EXAMPLE 7 jPoly(hexamethylene adipamide) is melt-spun at about 500 y.p.m. into a 'S4-filament yarn, and the yfreshly'formed yarn is immediately drawn and stabilized as in Example l. The apparatus employed is a modification of that shown in Figure 1 so .that the freshly formed yarn is supplied directly to feed roll 4 Without diversion (packaging, etc.) andv is drawn over pin 6 by the urging of draw roll 7. The drawn yarn is then passed into the oven 22 and over the driven metal rolls 25 and 26 (several passes) which, Yfor the purpose of setting freshly formed as-drawn yarn, ,areabout .6 inches in diameter. Hot air is used in the setting oven. After setting, the yarn passes to the relaxing roll 11, rather than back to the drawrroll -7. The usetting roll 9 is also by-passed. Relaxing roll 11 is run at a peripheral speed less than that of the setting idler rolls 25 and 26, hence the yarn is relaxed a controlled amount therebetween.

After stabilization, the yarn is wound onto a cylindrical core to form Van untapered package of .zero-twist yarn, utilizing conventional reciprocating traverse means (not shown). Optionally, the windup may be driven at a surface speed less than that of the relaxing roll 11, providing Aan additional stepwiseY relaxation. In fact, the relaxing roll 11 may be omitted altogether, with the relaxation being accomplished between oven'22 and windup. The relaxing means shown in Figures 3 and 4 may be employcd, between setting oven 22 and relaxing roll 11 Yand/ or the windup, although such means are not alwaysnecessary if the yarn is Vsutliciently warm from setting. These latter variations are possible through the use of freshly formed yarn. Results of these stabilizing procedures are given in Table VI. All yarns are wound onto the package at 0.24 g.p.d. tension; setting time in all cases is 0.13 second. The setting rolls 25 and 26 are run at `the same speed, somewhat higher than that of draw roll 7, so that some additionalV drawing (ca. 1.5 times) ,takes place between draw roll 7 and first setting roll 25. kFinal yarn denier is about 70.

l Control yarn, unset and unrelaxed. 2 Relaxed between oven 22 and windup (no relaxing roll).

3 Fitelared 2% between oven 22 and roll 1l, 1% between roll'll and Win up.

4 Relaxed 3% between oven 22 and roll 11 (with saturated atomospheric steam), 1% between roll Hand windup. Y

The on-the-package uniformity of the yarns DC, DD, and DF is excellent Vas is that fof yarn DE due to its exceptionally high initial modulus.

EXAMPLE 8 Selected yarns from the preceding examples are woven intoA .plain-weave rtaifeta .fabrics .of 104 x 7.6`construction. Representative fabric samples are viewed under indirect lighting,.and the presence .and .extent of Ypirn taper barr, quilizibarr, warp streams, etc., are noted.l The results of 'these observations arereported in Table VII.

Warp: moderate warp streaks.

set and relaxed, tests AD to Filling: free of plrn taper barr, AF, BB to BD, CG to no quill barr, no short'length streaks, no quill junctions.

OF, and yarn from Ex- Warp: mild warp streaks.

amples 4 and 5.

The process of this invention has been illustrated (Figure l) by reference to an apparatus wherein separate draw, setting, and relaxing rolls are employed, or, alternatively', the arrangement of Figure 5 is utilized for setting. However, a more compact and economical apparatus arrangement for accomplishing the setting and relaxing of this invention is shown in Figure 6. In this arrangement draw roll 28 is of stepped construction, having a portion of larger diameter indicated at 7, and a portion of reduced diameter indicated at 29. Separator roll 8 functions in cooperation with the larger portion 7 of the draw roll 28, and the supplemental separator roll 30 cooperates with the reduced diameter portion 29 of the draw roll 28. Idler rolls 25 and 26 are enclosed in oven 22 (Figure 5). Separator roll 27 feeds yarn from the enlarged portion 7 to reduced diameter portion 29 of the draw roll 28, and yarn passing to the separator roll 27 encounters a steam jacket 1S or oven 22, such as shown in Figures 3 and 4, in

zone e.

lnv operation, yarn 1 drawn in snubbing contact with pin 6 passes in multiple wraps about the enlarged portion 7 of the draw roll 28 and the separator roll 8, and passes from the enlarged portion 7 ofthe draw roll 28 about the idler rolls 25 and 26 in multiple wraps, and is thereby set in zone f. The yarn then passes Vfrom idler roll 25 back to the enlarged portion 7 of the draw roll 28, then traverses the steam jacket 18 in zone e, encounters the separator roll 27, and passes in multiple wraps over the smaller diameter portion 29 of the draw roll 28 and the separator roll 30, and is thereby relaxed to an extent proportional to the ratio of diameters of roll steps 7 and 29. The stabilized yarn, guided by pig-tail 13, is wound as shown in Figure l.

An improvement on the apparatus of Figure 6 comprises placing a thick insulated spacer between portions 7 and 29 of draw roll 28. Enlarged portion 7 together with its separator roll 8 may then be located Within an oven 22 (Figure 5). The insultated spacer Vlies in the plane of the wall of oven 22, so that reduced diameter portion 29 of draw roll 28 is without the oven, as are separator rolls 27 and 30. -In this arrangement, steam jacket 18 in zone e, idler rolls 25 and 26, and the oven 22 in zone f are not used. In operation, yarn is set between rolls 7 and 8 in oven 22, and relaxed between rolls 27and 29. Yarn is suiciently warm from setting that no additional heating is required in zone e on the way tofseparator roll 27. In such a manner the process of this invention is carried out with a minimum of apparatus, space, and cost.

The function of the insulated spacer between portions 7 and 29 of draw roll 28 is to insure that portion 29 of draw roll 28 remains cool during operation. Similarly, when using the apparatus of Figure l or any modications thereof, relaxing roll 11 Should also run cool, i.e., at about room temperature. Otherwise, relaxation cannot be controlled, since heat would be transferred from the relaxing roll to the yarn, .permitting additional yarn relaxation. Moreover, except when stabilizing freshly formed yarn, the yarn should be allowed to cool prior to packaging in order that shrinkage and mechanical property uniformity Vare not adversely affected.

A controlled relaxation of about 2% to 10% is coupled with setting in order to obtain the stabilized yarn of this invention. It is important that such relaxation be controlled, e.g., by roll or windup speeds, since otherwise yarn uniformity is decreased rather than improved. Attempts to relax yarn greater than lead to poor operability, diminished initial modulus, and shelling of the yarn from the package. Only marginal benefit is obtained from relaxing pre-packaged yarn less than about 6% or, in the case of freshly formed yarn, less than about 2%.

When stabilizing freshly formed or as-spun yarn, many variations in the stabilizing process are possible. This is possibly due to the fact that freshly formed yarn is relatively amorphous. These factors result in a uniform yarn which is most amenable to stabilization, since the controlled development of crystallinity takes place after structural non-uniformities or stresses are relieved through stabilization. Accordingly, (see Table VI) such yarn can be relaxed with (DF) or without (DB-DE) additional heating, in a single step (DB-DD), or in more than one step (DEDF). In addition, setting ca n be accomplished with dry heat with results approaching those obtained with steam. Note the use of relatively large metal rolls in Example 7 to increase the etciency of dry-heat setting. Finally, stabilized yarn having initial moduli increased 1.5 times or more can be obtained.

Yarn stabilized according to this invention is characterized by having reduced residual shrinkage and retained or increased initial modulus. In addition, the optimum stabilized yarns, e.g., AE, AF, CE, DF, etc., are extremely uniform, as evidenced by measurements of interiilament birefringence uniformity, improved about four fold or more over that of the control yarns AA, BA, CA, and DA.

The preferred levels of relaxation may be achieved stepwise or in a single step. With freshly formed yarn, additional heating after setting is not always necessary. Otherwise, moderate steam temperatures are sufficient; when using superheated steam at about 150 C., relaxation occurs in less than a tenth of a second. As shown in Examples l and 3, such relaxation may occur either prior or subsequent to setting, although the latter procedure is preferred.

Yarn which has been set, but not relaxed, is characterized as having reduced residual shrinkage (ca. 20% or more) with retained, or indeed, in some cases increased initial modulus. Such a yarn is useful in some less demanding applications.

Additional setting and relaxing agents useful in this invention include the mild swelling agents disclosed in U.S. 2,157,119, e.g., hydroxylated non-solvents for nylon such as methanol, ethanol, and the like. Also useful are high temperature liquid baths, with the proviso that such liquids are inert towards the yarn. Mineral oil, molten metal, or the like may be used in such baths. The conditions of temperature and duration of yarn exposure to these additional stabilizing agents are determined by routine experimentation.

The process of this invention is useful in preparing spindle-wound packages having a variety of contours, such as bottle bobbins, filling wind bobbins, headed spools, and the like. In addition, the present process is useful in draw winding operations wherein squareor tapered-shoulder packages of zero-twist yarn are wound upon cylindrical cores, using conventional reciprocating traverse means during winding. By employing the process of this invention in these operations, accomplished essentially as described in the foregoing, but with added tensioning means inserted between the relaxing system and the windup, it is possible to wind freshly drawn yarn onto inexpensive, disposable paper cores, heretofore impossible because of the compressive forces developed in packages of unstabilized yarn. By providing a one-way shipping package in a single operation, large savings are realized, since repackaging prior to shipping becomes unnecessary, or the need for extremestrength cores is obviated.

The process of this invention is especially useful with yarn composed of synthetic linear polyamides, such as those disclosed in U.S. 2,071,250 or U.S. 2,071,253 to Carothers. The preparation and Spinning of these compounds is in U.S. 2,130,948; 2,163,636; and 2,477,156. Examples of such polyamides are those prepared from suitable diamines and dibasic acids, e.g., from hexamethylene diamine and adipic acids; also comprehended are polyamides prepared from terminal-amino carboxylic acids, and their amide-forrning derivatives, e.g., polycaproamide from E-caprolactam. Yarn counts may range from monofilament yarn to yarn having any number of filaments. High denier yarn usually requires longer exposure and/or higher temperature during stabilization to compensate for the greater mass of the filament bundle.

The process of this invention permits preparing yarns having an initial modulus of at least about 27, residual shrinkage of less than about 7%, and maximum taperto-barrel difference in stretch tension of less than about 6, or in the case of zero-twist yarn applied to a straight package, a maximum range in residual shrinkage through the package of less than about 0.3%. Indeed, within the preferred limits of this invention it is possible to prepare yarn having an initial modulus of at least about 30 and a residual shrinkage of less than about 6% within the same ranges of uniformity. Both yarns, and particularly the latter, are exceptional in on-the-package uniformity of properties, may be wound onto inexpensive, disposable cores to form packages stable to shipping and handling, and the fabrics prepared therefrom are notably free from pirn taper barr and the similar fabric defects.

The claimed invention:

1. A process comprising partially setting a freshly drawn polyamide strand at substantially constant length while permitting a subsequent substantial reduction in residual shrinkage by relaxation without the usual decrease in initial modulus, relaxing the strand in a controlled manner in an amount between about 2% and about 10%, based upon the length of the strand immediately prior to relaxation, the setting and relaxing steps being carried out in any order, and then winding the strand onto a package.

2. The process of claim 1 in which the polyamide strand is a polyhexamethylene adipamide yarn.

3. The process of claim 1 in which the strand is set with heat.

4. The process of claim 1 in which the partial setting step precedes the relaxing step.

5. The process of claim 4 in which the strand is a polyhexamethylene adipamide yarn.

6. A process comprising removing a polyamide strand from a package, drawing the strand, partially setting the freshly drawn strand at substantially constant length while permitting a subsequent substantial reduction in residual shrinkage by relaxation without the usual decrease in initial modulus, relaxing the strand in a controlled manner in an amount between about 6% and about 10%, based upon the length of the strand immediately prior to relaxation, the setting and relaxing steps being carried out in any order, and then winding the strand onto a package.

7. The process of claim 6 in which the polyamide is polyhexamethylene adipamide and the strand is partially set by heating to between about C. and about 225 C. with steam and the strand is relaxed in an amount between about 7% and about 9% based upon the length of the strand immediately prior to relaxation.

8. A process comprising drawing a freshly spun polyamide strand, partially setting the freshly drawn strand at substantially constant length while permitting a subsequent substantial reduction in residual shrinkage by re- 15 laxation without the usual decrease in initial modulus, relaxing the strand in a controlled manner in an amount betweenabout 2% and about V6%, based vupon the length of the strand immediately prior to relaxation, the setting and relaxing steps beingcarried out in any order, and then winding the strand onto a package.

9. The process of claim 8 in which the polyamide is polyhexamethylene adipamide and the strand is partially set by heating to between about 170 C. and about 250` C. Vfor less than about one second with dry heat and the strandis relaxed in an amount between about 2% and about 4%, based uponthe length of the strand immediately prior to relaxation.

10. A polyamide strand package in which the strand throughout its length has an initial modulus of at least about 27, residual shrinkage of less than about 7%, and maximum taper-to-barrel difference in stretch tension of less than about 6.

11. The polyamide strand ,package of -claixn `10 in which ythe strand .is a polyhexamethylene adiparnide yarn.

12. The polyamide strand package of claim 10 in which thestrand is a polycaproamide yarn.

Y13.A polyamide strand package in 'whichthe strand throughout its :lengthhas anirritial modulus of at least aboutV 27, residual shrinkage `of less than about 7%, and maximum .range in residual shrinkage through the package of less than about 10.3%

' fl4. The polyamide strand package of Vclaim 13 in which .the strand is a polyhexamethylene adipamide yarn.

15. Thepolyamide strand package of claim 13 in which the strand is a polycaproamide yarn.

16. The process of Vclaim 4 in which the yarn being treated is vfreshly 'formed and the relaxation step occurs during windup of the yarn.

References Cited in the le of this patent f UisuTED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF vCORRECTION Patent No., A2995655330 October 18gr 1960 Gilbert Pitzl It is hereby certified that error appears in the-printed specfcatio: of the above numbered patent requiring correction and that the said Letter: Patent should read as corrected below.

line le/L1 for term"setting" as" read am term settng" as =-g column l line 29g for yaractionalw read fricti'onal MA; col 5\Y-\line lll for over read @e oven meg column i line 59, for "yarn drawn" read m drawn yarn Ag column 7i line?E for narcuatev read D accurate ====g column 9v line 70\7 for "stream" read m steam 45 column ll@ line lR for Mjunction read m junctions au; column l2Y line 53Ek for ainsultated" read ma insulated mm,

Sd and sealed this 11th day of April 1961u (SEAL) Attest:

ERNEST W. SWIDER ARTHUR W. CROCKER Attesting Ofcer Acting Commissioner of Patent 

1. A PROCESS COMPRISING PARTIALLY SETTING A FRESHLY DRAWN POLYAMIDE STRAND AT SUBSTANTIALLY CONSTANT LENGTH WHILE PERMITTING A SUBSEQUENT SUBSTANTIAL REDUCTION IN RESIDUAL SHRINKAGE BY RELAXATION WITHOUT THE USUAL DECREASE IN INITIAL MODULUS, RELAXING THE STRAND IN A CONTROLLED MANNER IN AN AMOUNT BETWEEN BOUT 2% AND ABOUT 10%, BASED UPON THE LENGTH O THE STRAND IMMEDIATELY PRIOR TO RELAXATION, THE SETTING AND RELAXING STEPS BEING CARRIED OUT IN ANY ORDER, AND WHEN WINDING THE STRAND ONTO A PACKAGE. 